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lkdtm: Add REPORT_STACK for checking stack offsets 

For validating the stack offset behavior, report the offset from a given
process's first seen stack address. Add s script to calculate the results
to the LKDTM kselftests.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210401232347.2791257-7-keescook@chromium.org
This commit is contained in:
Kees Cook 2021-04-01 16:23:47 -07:00 committed by Thomas Gleixner
parent fe950f6020
commit 68ef8735d2
6 changed files with 57 additions and 0 deletions
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17
drivers/misc/lkdtm/bugs.c
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@ -134,6 +134,23 @@ noinline void lkdtm_CORRUPT_STACK_STRONG(void)
__lkdtm_CORRUPT_STACK((void *)&data);
}
static pid_t stack_pid;
static unsigned long stack_addr;
void lkdtm_REPORT_STACK(void)
{
volatile uintptr_t magic;
pid_t pid = task_pid_nr(current);
if (pid != stack_pid) {
pr_info("Starting stack offset tracking for pid %d\n", pid);
stack_pid = pid;
stack_addr = (uintptr_t)&magic;
}
pr_info("Stack offset: %d\n", (int)(stack_addr - (uintptr_t)&magic));
}
void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void)
{
static u8 data[5] __attribute__((aligned(4))) = {1, 2, 3, 4, 5};

1
drivers/misc/lkdtm/core.c
View File

@ -110,6 +110,7 @@ static const struct crashtype crashtypes[] = {
CRASHTYPE(EXHAUST_STACK),
CRASHTYPE(CORRUPT_STACK),
CRASHTYPE(CORRUPT_STACK_STRONG),
CRASHTYPE(REPORT_STACK),
CRASHTYPE(CORRUPT_LIST_ADD),
CRASHTYPE(CORRUPT_LIST_DEL),
CRASHTYPE(STACK_GUARD_PAGE_LEADING),

1
drivers/misc/lkdtm/lkdtm.h
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@ -17,6 +17,7 @@ void lkdtm_LOOP(void);
void lkdtm_EXHAUST_STACK(void);
void lkdtm_CORRUPT_STACK(void);
void lkdtm_CORRUPT_STACK_STRONG(void);
void lkdtm_REPORT_STACK(void);
void lkdtm_UNALIGNED_LOAD_STORE_WRITE(void);
void lkdtm_SOFTLOCKUP(void);
void lkdtm_HARDLOCKUP(void);

1
tools/testing/selftests/lkdtm/.gitignore vendored
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@ -1,2 +1,3 @@
*.sh
!run.sh
!stack-entropy.sh

1
tools/testing/selftests/lkdtm/Makefile
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@ -5,6 +5,7 @@ include ../lib.mk
# NOTE: $(OUTPUT) won't get default value if used before lib.mk
TEST_FILES := tests.txt
TEST_PROGS := stack-entropy.sh
TEST_GEN_PROGS = $(patsubst %,$(OUTPUT)/%.sh,$(shell awk '{print $$1}' tests.txt | sed -e 's/\#//'))
all: $(TEST_GEN_PROGS)

36
tools/testing/selftests/lkdtm/stack-entropy.sh Executable file
View File

@ -0,0 +1,36 @@
#!/bin/sh
# SPDX-License-Identifier: GPL-2.0
#
# Measure kernel stack entropy by sampling via LKDTM's REPORT_STACK test.
set -e
samples="${1:-1000}"
# Capture dmesg continuously since it may fill up depending on sample size.
log=$(mktemp -t stack-entropy-XXXXXX)
dmesg --follow >"$log" & pid=$!
report=-1
for i in $(seq 1 $samples); do
echo "REPORT_STACK" >/sys/kernel/debug/provoke-crash/DIRECT
if [ -t 1 ]; then
percent=$(( 100 * $i / $samples ))
if [ "$percent" -ne "$report" ]; then
/bin/echo -en "$percent%\r"
report="$percent"
fi
fi
done
kill "$pid"
# Count unique offsets since last run.
seen=$(tac "$log" | grep -m1 -B"$samples"0 'Starting stack offset' | \
grep 'Stack offset' | awk '{print $NF}' | sort | uniq -c | wc -l)
bits=$(echo "obase=2; $seen" | bc | wc -L)
echo "Bits of stack entropy: $bits"
rm -f "$log"
# We would expect any functional stack randomization to be at least 5 bits.
if [ "$bits" -lt 5 ]; then
exit 1
else
exit 0
fi